1. Field of the Invention
The present invention is directed to a breathing apparatus, such as a ventilator or an anesthetic apparatus, wherein breathing gas is delivered to and removed from a respiratory system at the same time as the pressure and flow of the breathing gas is being measured, at least during delivery of the breathing gas, as well as to a method for controlling such a breathing apparatus.
2. Description of the Prior Art
Breathing apparatus supplying a breathing gas to a respiratory system (in humans or animals) and carrying expired breathing gas out of the respiratory system must be controlled in some way in order to avoid risks of damage to the respiratory system. In particular, the supply operation must be appropriately controlled. Preventing an excessive rise in pressure is essential, since excessive pressure could cause barotrauma. In a corresponding manner, supplying large volumes f gas to the respiratory system could cause volutrauma.
This is particularly the case in the ventilation of patients with diseased or damaged lungs. Ventilators connected to the patient's lungs are generally equipped with, or connected to, flow and pressure meters. Pressure and volume in the lungs can thus be monitored with the aid of pressure and flow measurements.
One problem in monitoring a patient with respect to pressure and volume is that damage-causing levels of pressure and volume can vary from patient to patient. In some patients, damaging pressure builds up in certain parts of the lung, whereas pressure remains on a harmless level in other parts of the lung.
At the same time, pressure must not be allowed to drop too much in certain patients, since their lungs might then collapse, making it necessary to supply an extra large amount of breathing gas to re-open the lungs. Lung collapse can also be partial, i.e. only parts of the lungs collapse. Positive end expiratory pressure (PEEP), a greater than atmospheric pressure produced at the end of expiration, is sued for keeping the lung open until the following inspiration commences.
In addition, the patient must also be supplied with a sufficient amount of breathing gas. Breathing gas supplied can be designated in terms of the minute volume supplied.